Dysfunction of hemodialysis vascular access is one of the most important sources of morbidity in the US end-stage renal disease (ESRD) population. Nearly 15 percent of all ESRD patient hospitalizations address vascular access complications. The median time from initiating dialysis until hospitalization for vascular access failure in the U.S. is less than 18 months. The cost of this morbidity has been estimated to exceed $100 million per year. Arteriovenous fistulae (AVF) are believed to be the optimal type of long-term dialysis vascular access but are placed in a small proportion of patients. AVFs are surgically constructed autologous (without implanted synthetic materials) vascular connections which provide access to the circulatory system of end-stage renal disease patients so as to permit the performance of hemodialysis. A considerable proportion, however, of patients' AVFs fail ever to mature into useful vascular access after their surgical construction. Over the past decade surgical practice has shifted away from creation of autologous AVFs in favor of implementation of synthetic dialysis vascular access grafts which have a markedly shorter life span. This evolution has been attributed to the growing primary failure rate of AVFs. The determinants of AVF failure are not well understood. The current proposed cohort study will determine the risk factors for the failure of surgically constructed arteriovenous fistulae to become useful vascular accesses for the purpose of hemodialysis. The risk of failure of AVFs to develop into useful dialysis vascular accesses will be assessed for patients of differing risk factor profiles. In this fashion, patients at high risk for primary AVF failure will be described and important potentially modifiable risk factors identified. The information derived from this study promises to identify better the subgroup of dialysis patients most likely to benefit from AVF placement and potentially improve the techniques of access surgery. These, study outcomes may then reduce markedly, both, the incidence, morbidity and cost of vascular access failure in patients on hemodialysis.